Get the Cars CD. Then take a look at Arizona State Route 66, from Seligman to Peach Springs and westward to Kingman. If you're using Microsoft Streets you'll have to zoom in further than the length of the segment for it to appear. Look familiar?
Seligman most closely resembles the town in the movie and many of the geological formations were borrowed from New Mexico. The 90 or so mile loop is very driveable in a RV. Grand Canyon Caverns has a campground and is an interesting undeground cave, accessable by elevator.
Avoid the segment between Kingman and Oatman, over Sitgreaves Pass. It's about the same as it was in the 1920's, extremely narrow and lots of sharp turns and sudden dropoffs, but if you're up for adventure you might want to take the toad for a day trip from Laughlin to Oatman, then over the pass to Kingman before returning to the RV via the Interstate. Oatman is famous for it's "wild" burros, they roam freely and respond well to being fed handfills of feed you can get from gumball machines scattered around town. The Oatman Hotel is said to be haunted by the ghosts of Clark Gable and Carole Lombard, who spent their honeymoon night there.
Another intact segment is the National Trails Highway, also off of Interstate 40 between Mountain Springs Road and Ludlow. Along the way you'll pass through the largely but not completely abandoned towns of Amboy and Bagdad (home of the "Bagdad Cafe" from the 1990 movie of the same name).
Although not as thouroughly documented, you can continue west on the National Trails Highway (old Route 66) from Ludlow to Barstow, through town on Main Street, then looping south through Helendale to Victorville.
I've traveled all of this, and it's very do-able in a RV, except as noted for the stretch between Kingman and Oatman. Most of the road and it's surroundings look like it did when the Interstate bypassed it in the 1960s, and in general the surface is good. In California, on some of the lesser-traveled segments there are stretches where the underlying concrete slabs are buckling the asphalt, giving a bit of a buck-board ride. But nothing too outrageous.
Take a look at
http://www.theroadwanderer.net/ I highly recommend taking a look at it.